Grounding diagnostic plug during B.I.S.S adjustment

[Heavy-D]

In the VFAQ for setting idle with the BISS screwon a 1g, it says to ground a terminal on the diagnostic plug (its attatched to the fusebox under the dashboard). Now my question is by grounding it do I connect the other end to the negative side of the battery, or attach it to the metal frame of the car or something else?

 

[Auto RS T]

The metal frame of the car will work just fine, no need to run it to the negative side of the battery. Find yourself a bolt to clip on to and ground out the plug.